In an ultrawideband (UWB) wireless communication system, the shape of the temporal pulse is important to correct system operation. The shape of the temporal pulse is only maintained if the transmitting and receiving antennae have flat, non-dispersive frequency responses. Electrically long antennae, such as dipole antennae, that are one-half or one-quarter of the radiated resonant signal wavelength λ are efficient but they have dispersive frequency response. For a typical electrically long antenna, the antenna performance uniformity begins to drop off for frequencies more than about 20% removed from the center resonant frequency. Thus, the temporal pulses in the pulse train of the broadband signal are distorted in shape by the dispersion in the electrically long antenna. The pulse distortion of an electrically long antennae smears the pulse shape beyond recognition at the UWB wireless communication system receiver. Therefore, non-dispersive electrically short antennae are used in UWB wireless communication systems.
Unfortunately, the electrically short antennae, which are about one-tenth of the wavelength of the radiated resonant signal, are inefficient radiators of radio frequency energy and are also poor receiving antennae. The maximum range of currently available electrically short antennae can be less than a few miles compared to a maximum range of as much as 30 miles for currently available electrically long antennae. The UWB systems increase the output power of the transmitters to offset the inefficiency of the electrically short antennae.
The increased output power required for the electrically short antenna in UWB system is a drawback for military applications, which require portability and the ability to conceal the system from the enemy. The higher output power required by the electrically short antennae makes the UWB system too power hungry for many portable battery operated applications and the high output power is more easily detected by enemy in the region.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for UWB wireless communication systems to overcome the dispersion of the efficient electrically long antennae so they can be used in portable UWB wireless applications.